Cache file is not created

Hello!

I recently downloaded your plugin and I noticed, that on first run, when it tries to create the cache file, it fails to do so, because the root that is being used is with `http` instead of `https`

Otherwise the plugin works as expected, thanks for creating it!

I created a PR with the fix as well, I hope that's ok.

Start by locating the cache-file creation entry point and the code that constructs its root URL. Reproduce the first-run cache creation path and verify that the cache file is created when the RFC source uses HTTPS.

Written by the indexing model from the issue text.